1. Field of the Invention
Embodiments of the present invention relate, in general, to manufacturing processes of firearms and more particularly to the manufacturing of a combined barrel, chamber and action from a unitary piece of material.
2. Relevant Background
Fundamentally a firearm includes a barrel, a chamber and an action. A barrel typically includes an integral chamber which receives and supports a cartridge casing during firing. Cartridge sizes are identified by a standard specification defined by commercial standards organizations. A firearm intended for a particular caliber ammunition is manufactured so as to have chamber dimensions designed to accept the specified cartridge with clearances to ensure reliable functioning under expected operating conditions. Prior art chambers are formed with chambering reamers. A chambering reamer is a precision cutting tool made from tool steel or similar material that expands the diameter of the barrel bore to form the chamber. Forming a chamber with a reamer usually requires at least three successive cuts using at least three custom made reamers. This method is expensive and time-consuming. Furthermore, as is known to one skilled in the art of metallurgy, the reaming process cold-works the barrel, inducing stress which must be removed through heat treatment, which adds to the cost of production. Moreover, a chambering reamer depends on centering the cut on a pilot hole, which extends into the bore of the barrel, thus degrading concentricity of the chamber with respect to the bore if metal chips are allowed to build up in the pilot hole.
Once a chamber has been fashioned within the barrel, the barrel must be attached to an action. As is well known to one skilled in the relevant art, the action (also referred to herein as the bolt body) accepts a bolt, which serves to position and secure the cartridge in the chamber. According to techniques well known in the prior art, a barrel, with an integral chamber, is coupled to a separately existing action component. Typically this coupling is accomplished by screwing the barrel into the action. Once the barrel is attached to the action, a gauge is inserted to measure the distance between the bolt and the end of a theoretical cartridge that would reside inside the chamber. The distance between the end of the bolt and a cartridge is known to one skilled in the art as the headspace. Headspace in the manufacturing of a bolt action firearm is critical. If there is not enough headspace the cartridge will not properly fit inside the chamber and the bolt cannot be secured for firing. Conversely, if there is too much headspace the reliability of firing a cartridge will suffer as will accuracy of the weapon. Moreover, excessive headspace can create a dangerous situation.
According to one method of firearm manufacturing as known in the prior art, the determination of headspace as a critical manufacturing specification is addressed by using a headspace guide. A headspace guide consists of a go and a no-go gauge. The go and no-go gauges are cartridge like devices that fit within the chamber to measure headspace. The go gauge is slightly smaller in length than the no-go gauge. The difference in the two is the acceptance headspace variance. With the barrel and chamber attached to the action, the bolt is retracted in the action and a go gauge is inserted into the chamber. The bolt is then closed into the action thus pushing the go gauge into the chamber. If the bolt closes with the go gauge inserted into the chamber there is sufficient headspace. The bolt is then retracted and the go gauge is removed from the chamber. Next a no-go gauge is inserted into the action. The no-go gauge is slightly longer than the go gauge. Again, the bolt is pushed forward inserting the no-go gauge into the chamber. The inability of the bolt to close confirms that there is not excessive headspace. If the bolt closes with the no-go gauge inserted in the chamber then there is too much headspace creating a dangerous situation. The difference between the go gauge and no-go gauge is the maximum allowable headspace for the particular type of weapon.
While testing for proper headspace is relatively simple, correcting inadequate or excessive headspace is easier said than done. If there is inadequate headspace, the barrel is typically removed from the action and the length of the barrel is reduced as the length of the chamber is deepened by using a reamer. The barrel is once again attached to the action and the go gauge reinserted to test for sufficient headspace. Alternatively, the bolt face can be adjusted. While conceptually simple, these modifications are time-consuming and expensive.
To correct excessive headspace, the distance between the end of the bolt and end of the cartridge must be reduced. While the overall length of the barrel and chamber could be redesigned, a more likely approach to correcting excessive headspace is to increase the length of the bolt. As is known to one skilled in the relevant art, to correct excessive headspace by modifying the barrel, the barrel must be removed from the action and a portion of the end of the barrel, where the barrel attaches to the action, removed. Thus, as the barrel is again attached to the action, the cartridge sits slightly deeper in the action and headspace is reduced. With the newly dimensioned barrel attached to the action, the go gauge is again inserted into the chamber to verify that sufficient headspace exists. Thereafter the no-go gauge is inserted to verify that excessive headspace has been eliminated. This process may occur several times before an acceptable headspace is achieved.
The verification and sometimes correction of headspace is conducted on each weapon in the manufacturing process. This process is tedious and time consuming as well as expensive. The need therefore exists for a process to create a unitary barrel, chamber and action (bolt body) assembly eliminating the need for headspace correction. These and other improvements to the prior art are described below by way of example.